In the case in which a food is cooked by the high frequency heating of a microwave oven, conventionally, there is a drawback that a steam is generated from the food by the heating and a window glass of an opening door of a heating chamber is steamed up by the steam, and the state of progress of the cooking cannot be confirmed. As a countermeasure, there is widely employed a structure in which a wind supplied from an air supply port into the heating chamber is blown against the window glass of the opening door. For the wind at this time, in the case in which the outside air is directly introduced and blown against, a temperature in the heating chamber is greatly reduced. For this reason, warm air obtained after cooling a magnetron is used. Moreover, the steam generated from the food rises in a close position to the window glass of the opening door. Therefore, the air supply port is provided above the heating chamber which is close to the opening door and the wind is blown against the window glass from above. Moreover, an air discharge port for discharging the wind supplied from the air supply port is also provided in the heating chamber.
In the oven heating, however, the function of introducing the wind and discharging the steam through the air supply port and the air discharge port turns the air out of the heated inside of the heating chamber so that a heating efficiency is reduced. For this reason, there is required such a device that positions in which the air supply port and the air discharge port are to be disposed are changed or a shutter is provided in the middle of a passage. In order to reduce a cost, generally, the position in which the air discharge port is to be disposed is taken as the countermeasure, and the air discharge port is often disposed near a lower part on the inner side of the heating chamber. At present, thus, there is widely used a microwave oven with an oven function having a structure in which an air supply port and an air discharge port are provided in upper and lower parts of a side wall surface of a heating chamber.
By adding a steam generating function to the microwave oven of this type, it is possible to execute high frequency heating and steam heating at the same time or independently. In case of cooking in which the steam heating is mainly carried out, it is important that a suitable temperature for a food is ideally maintained in a state in which a steam density is approximately 100% (for example, 80° C. in case of an egg, 98° C. in case of a meat bun and 100° C. or more in case of a steamed potato) in order to successfully carry out cooking rapidly and reliably.
In a special steamer for steam cooking, a large amount of water is boiled to raise a steam density. By a structure in which a heating chamber is vertically divided by a dividing plate (a tray for mounting a food) in order to raise the steam density, thereby forming small spaces on the upper side of the heating chamber and supplying a steam to the spaces on the upper side in the microwave oven, however, it is possible to heat an object to be heated in a state in which the steam density is increased.
For example, Patent Document 1 has disclosed a steam cooking device for regulating a steam partial pressure (a volume ratio of occupation of the steam) in the heating chamber to set an atmospheric temperature in the heating chamber when carrying out cooking in which an accurate temperature management is important for the cooking as in egg cooking.
Patent Document 1: JP-A-63-254320 Publication